Critical Sampling in Pediatrics
Critical sampling refers to the collection of blood and other laboratory specimens during an acute clinical episode—specifically when a newborn presents with signs of hypoglycemia, metabolic decompensation, or surgical emergency—to capture diagnostic metabolic markers that may only be detectable during the acute illness state.
What Critical Sampling Entails
Critical sampling is performed when a neonate presents with concerning signs that may indicate an underlying metabolic disorder or surgical emergency. The timing is crucial because certain metabolic abnormalities are only detectable when the patient is symptomatic 1.
Key Clinical Scenarios Requiring Critical Sampling
- Hypoglycemia episodes - Blood should be drawn before glucose administration to capture insulin levels, ketones, lactate, and acylcarnitine profiles 1
- Metabolic decompensation - Including lethargy, poor feeding, vomiting, seizures, or altered consciousness 1
- Suspected surgical emergencies - When bilious emesis, abdominal distention, failure to pass meconium, or signs of bowel obstruction are present 2, 3
Essential Specimens to Obtain
When a newborn presents with potential surgical emergency signs, the following should be collected:
- Blood glucose - Must be obtained before any glucose administration 1
- Complete blood count with differential - To assess for infection or inflammatory processes 4
- Blood culture - To identify potential sepsis, which can mimic surgical emergencies 4
- Serum electrolytes, lactate, and ammonia - To detect metabolic disorders 1
- Urine for organic acids and acylcarnitines - If metabolic disorder suspected 1
Cardinal Signs Requiring Urgent Evaluation
The four cardinal signs of neonatal intestinal obstruction that should prompt immediate critical sampling and imaging include 3:
- Maternal polyhydramnios - Suggests upper GI obstruction 3
- Bilious emesis - Indicates obstruction distal to ampulla of Vater and requires urgent surgical evaluation 3
- Failure to pass meconium within first 24 hours - May indicate Hirschsprung disease, meconium ileus, or anorectal malformation 5, 3
- Abdominal distention - Can range from subtle to massive with respiratory compromise 3
Diagnostic Imaging Approach
Point-of-Care Ultrasound (POCUS) Applications
POCUS is helpful for detecting free intra-abdominal fluid, assessing bowel peristalsis, and identifying signs of necrotizing enterocolitis in neonates with suspected surgical emergencies 1.
Specific POCUS applications include:
- Detection of free intra-abdominal fluid - Highly sensitive for perforation or peritonitis 1
- Assessment of bowel peristalsis - Can identify ileus or obstruction 1
- Recognition of hypertrophic pyloric stenosis - Though definitive diagnosis requires pediatric radiology confirmation 1
- Detection of necrotizing enterocolitis signs - Including bowel wall thickening, pneumatosis, and portal venous gas 1
Advanced Imaging
- Plain abdominal radiograph - First-line for suspected bowel obstruction, showing gaseous distention and air-fluid levels 6, 3
- Abdominal CT scan - May be useful for establishing early recognition of late-onset NEC or other surgical emergencies 7
Common Pitfalls to Avoid
- Delaying specimen collection until after treatment initiation - Glucose administration before blood draw invalidates metabolic testing 1
- Assuming all abdominal distention is benign - Even term infants without risk factors can develop NEC or other surgical emergencies 7
- Relying solely on clinical signs - Neonatal presentations can be subtle and nonspecific, requiring low threshold for laboratory and imaging evaluation 4, 3
- Missing the window for metabolic diagnosis - Once the acute episode resolves, diagnostic markers may normalize and the underlying condition remains undiagnosed 1
Immediate Management Priorities
While awaiting results, concomitant resuscitation should include 3: